In a wireless network, connectivity and communication between devices is achieved through antennas attached to receivers or transmitters in order to radiate the desired signals to or from other elements of the network. In radio communication systems, such as millimeter-wave radios, discrete components are usually assembled with low integration levels. These systems are often assembled using expensive and bulky waveguides and package-level or board-level microstrip structures to interconnect semiconductors and their required transmitter or receiver antennas.
With recent progress in semiconductor technology and packaging engineering, the dimensions of these radio communication systems have become smaller and integration of antennas with their radio frequency (RF) front-end circuits has become more desirable. For applications such as wireless universal serial bus (USB), the operating distance is limited to about a meter; a single antenna with about 7 dBi at 60 GHz will provide the necessary antenna gains.
However, for point-to-point applications which require operating distances of ten meters (such as wireless video) or longer (such as military radar), antenna gains as high as 30 dBi may be required. However, because high-gain antennas have very narrow beam widths (thereby making it difficult for consumers to accurately point the antenna), phased arrays (also known as radiation pattern steerable arrays) are necessary. As is well-known to one having skill in the art, phased arrays typically comprise array radiating elements (such as microstrip patches, dipoles, folded dipoles and slots); a beam forming network (typically including phase shifters); and a controller.
For example, D. M. Pozar, “A microstrip antenna aperture coupled to a microstrip line,” Electron. Lett., vol. 21, pp. 49-50, Jan. 17, 1985, discloses an arrangement wherein a microstrip antenna on one substrate is coupled to a microstripline feed on another parallel substrate through an aperture in the ground plane which separates the two substrates. J. A. G. Akkermans, M. C. van Beurden, and M. H. A. J. Herben, “Design of a Millimeter-Wave Balanced-Fed Aperture-Coupled Patch Antenna,” Proc. ‘EuCAP 2006’, Nice, France, Nov. 6-10, 2006, discloses an arrangement wherein a balanced feed electromagnetically couples to a patch through two separate slots.